1989 Ford Ranger Rear Brake problem

I am currently working on this vehicle. My son is taking off all the brake lines due to the fact that they are rusted and have been replaced at least once before we bought the truck. Actually, the person before us cut out the bad line from the MC and the back and just left it on the truck.

Anyway, I removed the brake shoes and the wheel cylinders to put all new brake parts on this truck.
As I was cleaning the backing plate, I noticed that where the bolt openings to secure the wheel cylinder are are rusted out.

My questions are:

Do I need to replace the backing plate?

If yes, How?

If Not, would the bolts hold the wheel cylinder in place? They both rusted out on the inside edge and the bolt heads are bigger than the holes they go into.

Thanks!!

BTW I have an AS in Automotive Technology. My specialty is brakes but I've never had this happen.